Each papillomavirus is species specific and replicates persistently in a specific type of cutaneous or mucosal epithelium. The keratinocytes of the basal layer of the epithelium harbor a reservoir of replicating viral genomes and therefore are the ideal cells in which to study the mechanisms by which HPV establishes persistent infection. Papillomaviruses will only undergo their complete life cycle and generate progeny virus in the tissue culture equivalent of a stratified epithelium. This process requires establishing stably replicating viral DNA genomes in primary human keratinocytes and culturing them in three-dimensional skin equivalents. For our studies on HPV replication we wanted to develop an optimal replication system in keratinocytes so that we could study the requirements in the natural host. Alpha Papillomaviruses induce persistent epithelial lesions and are associated with the development of cervical cancer. The aims of this project are to determine the mechanism of extrachromosomal replication and partitioning of the viral genome. -We have established a treatment that allows us to efficiently immortalize primary human keratinocytes. -The immortalized keratinocytes are invaluable for studies on the long-term persistent viral DNA replication